Remotely tuned conductive-body antenna system

ABSTRACT

An improved remotely tuned conductive-body antenna system is provided which gives superior signal coupling between the low impedance conductive body and the associated radio-frequency circuits with minimum loss of selectivity or &#39;&#39;&#39;&#39;Q&#39;&#39;&#39;&#39; in those circuits by increasing the inductive reactance of the coupling means insofar as the associated radio-frequency circuits are concerned without mis-matching the input to the coupling means and the low impedance conductive-body signal source.

Davis Oct. 28, 1975 REMOTELY TUNED CONDUCTIVE-BODY ANTENNA SYSTEMInventor: Ross Alan Davis, 724 Ala Moana Primary E.vaminer-Eli LiebermanAttorney, Agent, or FirmBruce L. Birchard Blvd., Honolulu, Hawaii 96813[21] Appl. No 427,259

An improved remotely tuned conductive-body antenna system is providedwhich gives superior signal U-S- coupling between the low impedanceconductive Cl. and the associated radio frequency circuits mini- Fleld0f Search 712, 713, 856 mum loss of selectivity or Q in those circuitsby in- I v creasing the inductive reactance of the coupling [56]References ('lted means insofar as the associated radio-frequency cir-UNITED STATES PATENTS cuits are concerned without mis-matching the inputto 2,750,590 6/1956 Phelps 343/856 the Coupling means and the lowimpedance Conduc- 3,717,876 2/1973 Volkers et al. 343/712 y SignalSource- FOREIGN PATENTS OR APPLICATIONS 5 Ch'fims, 13 Drawing Figuresl,949,828 4/1970 Germany 343/712 1e l9 l I be 2| '2;

l l 82 28 I '28 9Q US. Patent- Oct. 28, 1975 Sheet 1 of4 3,916,413

5.1 qpL US. Patent 00:. 28, 1975 Sheet 2 Of4 3,916,413

US. Patent Oct. 28, 1975 Sheet 4 of4 3,916,413

'high impedance of the input circuits of the radio appa- REMOTELY TUNEDCONDUCTIVE-BODY ANTENNA SYSTEM RELEVANT COPEN DING APPLICATIONSApplication Ser. No. 427,258, filed Dec. 21, 1973, 5 now abandoned, bythis inventor and entitled Antenna System Utilizing Currents inConductive Body. Application Ser. No. 430,095 filed Jan. 2, 1974, bythis inventor and entitled Improved Radio Frequency Transformer.

BACKGROUND OF THE INVENTION In US. Pat. Nos. 2,923,813; 2,971,191;3,007,164 and 3,066,293 the present inventor described severalapproaches to utilizing as antennas conductive structures such asautomobile bodies. Because of the very unusual characteristics andextremely difficult problems encountered in extracting usable R.F.signals from existing conductive structures, the state of the art hasdeveloped only gradually through the years. This has been particularlytrue for the extraction from conductive structures, such as car bodies,of signals at lower frequencies in the region of the AM broadcast band.New and unique techniques have been required to extract a maximum ofthese elusive signals (correspond ing to the-magnetic component ofincident electromagnetic fields) from existing discontinuities andparticularly from the limited discontinuities formed in the fabricationof car bodies. Until recently, the art, even that developed by thisinventor, could not properly meet this challenge.

To fully appreciate the many steps of painstaking progress and the manytrials and errors involved in achieving the advancements in the artrepresented by the invention shown and claimed herein, it is desirableto trace the problems faced with the systems described in those patentsand how those problems were solved.

As is well known, radiated electromagnetic signals comprise twocomponents, the electrical component and the magnetic component. Thesignal component relied upon in the operation of the subject inventionis the magnetic component, as it was in the earlier-issued patents. Theimpedance looking into a discontinuity in an existing conductivestructure at radio broadcast frequencies is extremely low when such aconductive structure is that of a car body, the inductance being themajor part of that impedance with an average maximum of only 2micro-henries. Because of the relatively ratus coupled to thediscontinuity in the conductive body it was considered impracticable,(prior to the work of the inventor), to couple radio broadcast signalenergy efficiently out of a conductive body into associated radioapparatus, as for example, into an associated radio receiver.

To help solve this problem this inventor conceived and successfullyreduced to practice a unique voltage and impedance transformer usable atradio frequencies and comprising a one-turn conductive sheath or tubeacting as the primary of an auto-transformer, the secondary being formedby a conductor passing through the inner opening of the sheath or tube 8or 9 times (when used at AM broadcast frequencies) and, hence, beingvery tightly magnetically coupledto the single turn primary of theauto-transformer. This unique design reduces unwanted electrostaticsignals and noise in the transformation process. Further reduction ofnoise can be achieved by using a double-walled sheath, the inner wallproviding electrostatic-shielding, as described hereinafter. To furtherimprove the coupling between the single-turn primary and its secondaryand to increase the inductance of the single-turn primary to a levelsuch that it matches the inductance of the discontinuity in theconductive body, and, also, to further shield the transformer fromextraneous electrical signals, a series of ferrite, high-permeabilitybeads is applied so that it covers completely the one-turn primarysheath or tubing.

To simplify the discussion which follows, reference will be madefrequently to a car body as the conductive body which acts as theantenna for this system. It should be understood that any conductivebody, stationary or mobile, having an electrical discontinuity thereineither solely for the purpose of this system or performing otherfunctions as well, may be used in this system. In a car body, inaddition to desired signals there are many undesired noise signalsproduced by the ignition system and various other electrical equipmentfound in cars today. These noise signals are in common conductive pathswith the desired signals. Those noise signals have, in a majority ofcases, a large electrostatic component and, in early systems designed bythis inventor, the interference they produced made acceptable receptionof desired signals most difficult without extreme diligence in isolatingand eliminating the noise signals from the desired signal currents inthe common conductive structure. One method for raising the level of thedesired signals with respect to the undesired, or noise signals (beyondthat accomplished by the use of the R.F. auto-transformer describedherein), is to resonate to the desired-signal frequency the signalsource (the conductive body), as is shown and described in copendingapplication Ser. No. 427,258, filed Dec. 21, 1973, by this inventor. Asecond method is to tune the secondary of the auto-transformer to thefrequency of the desired signal. In both cases the inductance is verylow and the size of the capacitor required to resonate the inductancesat broadcast radio frequencies is very large and the range ofcapacitance variation required to tune across the broadcast band is verylarge (9 to 1) making the use of conventional variable capacitorsgenerally impracticable. This inventor then devised a system utilizingbanks of small capacitors switched in or out in single step fashionthrough a multi-fingered sliding contact device which was ganged to thevariable inductance or slug tuner in the radio and maintained theapproximate value required for resonance of the associated inductance.Unfortunately, the number of switching contacts required was excessivein parallel resonating the auto-transformer secondary and the switchingnoise produced in the radio input circuits was a problem that requiredregular service to maintain quiet operation of this tuner. As a result,in the early systems, fixed tuning was the only available solution andit provided less than optimum performance. Further work by this inventorresulted in the development of a simplified, variable, series-resonanttuner that was used in the tuning of the low-impedance primary of theauto-transformer to achieve maximum coupling of energy from a conductivebody discontinuity into associated radio apparatus. With this seriescapacity tuning, step switching was usable because of the low impedancein the primary. Switching noise was not objec tionable even in high-gaincar radio input circuits adapted for use with the subject car bodyantenna system. However, such tuning of the low-impedance primary, byitself, left much to be desired both in selectivity and signal voltagegain. Signal voltage gain is particularly important when the source is alow impedance conductive-body discontinuity, as it is in this case.Attempts to increase the voltage gain in the autotransformer byconventional means, such as by loosening the primary-secondary coupling(to reduce inherent inter-winding capacitance) and increasing the numberof primary and secondary turns were not entirely acceptable. Furtherdevelopment work by this inventor was necessary to achieve the requiredvoltage gain and Q in the circuits (and a better L/C ratio, particularlyin the low impedance input transformer used to further isolatetroublesome noise problems); and, finally, to permit a more simplifiedtuning of the antenna system remotely, as from the radio receiver in thecar, simultaneously with the tuning of that receiver, all withoutadversely affecting voltage gain and signal selectivity in the receiver.

This inventor then hit upon the idea of connecting the secondary tuningcondenser in the electrical center of the secondary winding of theauto-transformer with its tightly coupled, low-impedance primary andhigher impedance secondary. By locating the secondary tuning condenserin the electrical center of the secondary, (whether that secondary islumped in the matching transformer or distributed along the border of adiscontinuity), the effective distributed capacity of the secondary isreduced sharply and the number of turns on that secondary may beincreased for a given desired frequency of operation, thus permittinggreater voltage gain in the transformer and permitting the remotelocation of the secondary-tuning capacitor through extended shieldedcables. It should be noted that in the lumped auto-transformer thesecondary is contained within (and is electrostatically shielded by) thesingle turn tubular primary. An additional tube or sheath may beprovided for electrostatic shielding. Further, the primaryis encasedwith ferrite material to produce a primary inductance which is matchedto the source of signal; viz., the conductive body discontinuity, sothat maximum signal current flow may be produced in the single turnprimary. (The full voltage available from the discontinuity is appliedacross this one-turn primary).

To further advance and simplify this body (magnetic) signal techniqueand at the same time make it fully adaptable to todays standard highimpedance car radio inputs (with a minimum of required changed andincreased costs), a very practical combination of car body magneticsignals and electrostatic signals from a conventional antenna has beenmade. This combination simplifies adapting this inventors car-bodysignal techniques to use with standard radio receiver input circuits.This combination further reduces the need for dual magnetic signal inputto the associated radio receiver so that a single conductive-body-signalinput may be used when properly combined with a high impedanceelectrostatic antenna input. Also additional performance features havebeen gained over both the electrostatic and magnetic systems, which arenot available from either separately. This added signal input can bederived from the simple addition of an insulated fine wire antennaimbedded in the windshield (or rear window) as is currently being donein both American made and American imported cars. The magnetic conductive-body signal may be derived by magnetic induction from the perimeterof the same windshield or rear window to reduce costs and simplifymanufacture. Or, as

described in patent application Ser. No. 427,258 of this inventor, thecar-body magnetic signal may be taken from a structural element adjacentthe windshield or rear window. One of the unusual assets gained in thiscombination of electromagnetic and electrostatic signals is that furthernoise reduction can be achieved when R. F. noise from the two sources isproperly phased and balanced as shown and described herein. Furthergreater extended signal range can be now accomplished by thiscombination, thus increasing the practicability of the insulatedwindshield wire antenna which is known for its limited ability tofunction in poor signal areas. The electrostatic antenna also suffersfrom sharp signal attenuation in structural, overpass and mountainousareas. To further enhance this combination of signal sources, afunctional switch can be added to allow switching in either systemseparately or in combination. This switching capability is also usefulin demonstrating the superior performance of the carbody antenna withrespect to the insulated wire electrostatic antenna in variedsituations.

Another method for improving the coupling of the signal from the bodysource to the relatively high impedance receiver input circuits is thedouble-ended driving of the extended primary of a transformer having acorrespondingly larger secondary winding, as described hereinafter.

It should be noted that the antenna system described herein may be usedequally well in the transmitting 35 mode as in the receiving mode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a representation, partiallyas an elevational view and partially as a schematic diagram of anantenna system according to the present invention;

FIG. 2A is a representation, partially in elevation and partially inschematic form of a second antenna system incorporating the presentinvention;

FIG. 2B is a schematic representation of a variation in the antennasystem of FIG. 2A;

FIG. 3A is a representation, partially in elevation and partially inschematic form of a third form of antenna system incorporating thepresent invention;

FIG. 3B is a schematic diagram of a variation of the antenna system ofFIG. 3A;

FIG. 4A is a schematic diagram of an additional variation of an antennasystem according to the present invention;

FIG. 4B is a circuit diagram showing variation of the antenna system ofFIG. 4A;

FIG. 5 is a diagram, partially in schematic form, of an antenna systemfor deriving dual tuned signals from a single discontinuity;

FIG. 6 is a partially schematic diagram of an antenna system accordingto the present invention utilizing existing functional elements of anautomobile for disguising the antenna coupling element;

FIG. 7A is a schematic diagram of a first doubleended primary drive forthe transformer in an antenna system according to the present invention;

FIG. 7B is a schematic diagram of a variation in the coupling systemutilized in FIG. 7A;

FIG. 8 is a schematic diagram of a transformerless double-ended signalcoupling circuit according to the present invention; and

FIG. 9 is a schematic diagram of a dual source coupling system accordingto the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS In FIG. 1 conductivebody 10 has opening 11, therein. For purposes of convenience body 10 isshown as a car body and opening 11 may be a front or a rear windowtherein. Opening 11 is bounded by conductive edge 12 along whichradio-frequency currents flow when body 10 is exposed to aradio-frequency energy field. As a result of such current flow aradio-frequency potential difference exists between points 13 and 14along edge 12. Further, because of the close proximity of conductors 15,16, 17 and 18 to edge 12 (they may actually be hidden under the trimwhich normally covers edge 12 for aesthetic purposes) that portion ofedge 12 between points 14 and 13 on the side proximate to conductors 15,16, 17 and 18 is inductively coupled to those conductors and may beconsidered, along with exciter lead 19, to be the primary of anautotransformer of which conductors 15, 16, 17 and 18 constitute thesecondary. This secondary is tapped by means of conductors 20 and 21more or less at its center point. The tapping point may vary from theexact center point without departing from the essence of this invention.As conductors 20 and 21 emerge from shielding sheath 22 they are coupledacross variable condenser 23. Variable condenser 23 may be ganged withmain variable inductance or slug tuner 25 which is shunted by trimmer24. Slug tuner 25, has coupled thereto winding 26 which transfers energyto or from associated electrical circuits for receiving or transmittingradio-frequency signals. Coupling condenser 27 may, by reason of thecentral tuning of the secondary comprising conductors 15, 16, 17 and 18,be from 20 to 100 pico-farads without destroying the selectivity of thetuned circuit comprising condenser 24 and inductor 25.

Padding condenser 29, which may be of a magnitude of 0.01 micro-faradsis coupled between end terminal 30 of the autotransformer made up ofconductors through 18, and edge 12 in the region of point 14. Therelative capacitance of padding condenser 29 and cou pling condenser 27determines the portion of the total signal voltage introduced into slugtuner 25. In addition to the signal picked up from the R. F. currentsflowing in edge 12, a separate sense antenna 31 may be provided. This isessentially an electrostatic pick-up device which may be embedded in theglass placed in opening 11. The signal from this antenna is carried byconductor 32 to terminal 33 of a two-pole triple-throw selector switchincluding fixed contacts 33, 34, 35, 36, 37 and 38 and movable contacts39 and 40. With the selector switch in the position shown both the carbody signal and the sense-antenna signal are fed through noise filterchoke 40' to the radio receiver input tuned circuit. With the selectorswitch moved to the left in FIG. 1, i.e., with movable contact 39connected to fixed contact 35 and movable contact 40 cooperating withfixed contact 36, only the car body signal is coupled to the receiverinput circuit. With the selector switch moved to the right, i.e., withmovable contact 39 connected to fixed contact 33 and movable contact 40connected to fixed contact 38, only sense-antenna 31 is in use. In somesituations the combination of the signals from the sense antenna and thecar body gives optimum results. Sometimes the best signal is derivedfrom the car body alone. Occasionally it may be desirable to use thesense antenna alone. The switching system of FIG. 1 permits theselection of optimum signal strength.

The size of the wire used for conductors 15 through 19 can be variedbetween 18 and 40 gauge with the criteria being minimal obstruction ofvision through opening 11 and minimum resistance in the secondarycomprising conductors 15 through 18 In FIG. 2A the secondary of theauto-transformer is disposed in both halves of opening 11. Conductor200, in combination with edge portions 201, 202 and 203, constitutes theprimary of a first half of the secondary comprising conductors 207 and208, and conductor 200, in combination with edge portions 204, 205 and206, constitutes the primary of a second half of the secondarycomprising conductors 209 and 210. The method for tuning the inductanceappearing between center-tap conductors 211 and 212 and for couplinginto and out of associated radio apparatus is the same as that describedin connection with conductors 20 and 21 of FIG. 1, and need not berepeated here. Early experiments have indicated that the secondarydisposition described in connection with FIG. 2A may reduce noisesignals arising from local sources, such as the automobile ignitionsystem. Sense antenna 213 is provided for the same purpose and with thesame results described for sense antenna 31 in FIG. 1. It is coupledthrough conductor 214 to a selector switch comprising fixed contacts 215through 220 and movable contacts 221 and 222. This selector switchperforms the same function as the selector switch of FIG. 1.

In FIG. 2B the extraction of desired magnetic signals from the car bodyis accomplished by means of inductive coupling from edge portions 230through 233, which constitute the primary of a transformer, of whichconductors 234, 235, 236 and 237 constitute the secondary. Thiscombination differs from the structure of FIG. 2A in that there is nodirect connection to the boundary of the discontinuity 238. Theadvantage of this configuration is that the conductive noise currentswhich might be mixed with signal currents in the body and areconductively isolated from the radio input circuits, because onlyinductive coupling transfers signals from the primary to the secondary.A single ground point for the input circuits further limits andconductively isolates these troublesome noise currents. The secondary isbalanced as in FIG. 2A, and similarly has a figure-eight configuration.Central tuning of the secondary is accomplished, remotely, in thefashion de scribed in connection with the antenna system of FIG. 2Autilizing condenser 239 coupled through conductors 240 and 241 to the R.F. transformer secondary made up of conductors 233 through 237. Theleads to the remote circuits are shielded from noise pick-up byconductive sheath 241'. Sense antenna 242 may be provided and functionsas described in connection with FIG. 2A.

In FIG. 3A the secondary tuning concept of this invention is shownapplied to an antenna system of the type disclosed in co-pendingapplication Ser. No. 427,258 entitled Antenna System Utilizing Currentsin Conductive Body and filed by this inventor on Dec. 21, 1973.

In FIG. 38, column 300 in a conductive body has an impedancediscontinuity therein produced by severing the column, using ferrite inand around the column or increasing its resistance in a region,resulting in the appearance of an electrical potential across points 301and 302. Sheath 303, of copper or other conductive material is connectedat its extremes 304 and 305 to points 301 and 302, respectively, andacts as the primary of an auto-transformer for which conductors 306 and307 form the secondary. The secondary is split at points 308 and 309 andis coupled by means of connectors 310 and 311 to tuning condenser 312which may be ganged with variable inductance 315. lnductance 315, inturn, is shunted by trimmer 313. This coupling network functions in thesame fashion as that described in connection with FIG. 1 and need not bedescribed further here.

Ferrite material 314 may be applied to sheath 303 to provide magneticshielding and to increase the coupling of the primary and secondaryportions of the auto-transformer. Sheath 303, its ferrite covering 314and the conductors 306 and 307 may be made aesthetically more attractiveby incorporating them in a mirror, for example, mounted on column 300,taking care not to short circuit the desired impedance discontinuity incolumn 300.

In FIG. 3B auto-transformer 320 is located remotely from thediscontinuity in the conductive body but is coupled thereto by coaxialcable 321 having central conductor 322 and conductive sheath 323.Central conductor 322 is connected to point 324 and conductive sheath323 is connected to point 325 on opposite sides of discontinuity 326 incolumn 300. Thus, the full R.F. potential appearing between points 324and 325 is applied across coaxial cable 321. While a coaxial cable hasbeen found to perform best in this coupling directly to the lowimpedance signal source, strictly speaking a coaxial cable is notrequired but merely an internal conductor insulated from an outerconductive sheath may be used when of good design for R. F. en-

ergy transfer. The outer sheath, in either case minimizes noise signalpickup from surrounding noise sources when correctly grounded at bothends.

In FIG. 3B, auto-transformer 320 functions as does the auto-transformerdescribed in connection with FIG. 3A. However, it is often inconvenientto mount the auto-transformer at the body discontinuity. This inventorhas found, surprisingly, that the remote location of auto-transformer320 not only performs an effective impedance and voltage transformationbut also produces a significant noise reduction by reason of theshielding and electrostatic isolating effect of outer tubing or sheath327 which also constitutes the one-turn primary of auto-transformer 320.The remote location of transformer 320 also allows conductive isolationfrom undesirable noise currents flowing with the desired signal currentsin the conductive structure. Additional shielding sheath or tube 328provides further noise suppression by isolating the primary andsecondary portions of transformer 320, electrostatically, from eachother. This system has proven in tests to be very effective in cars withhigh levels of locally generated noise. The remainder of the circuit ofFIG. 38 operates in the same fashion as the circuit of FIG. 3A.

In FIG. 4A the signal potential produced between points 401 and 402 onopposite sides of discontinuity 403 in column 404 is applied toconductors 405 and 406 of coaxial cable 407. Sheath 406 is grounded atthe receiver end, as shown. Center conductor 405 is coupled throughseries tuning condenser 408 to primary coil 409 of input transformer410, the secondary 411 of which is core or slug tuned. Condenser 408 andthe movabie core which tunes secondary 411 may be ganged. Noise transferfrom primary 409 to secondary 411 is prevented by electrostatic shield412. Inherently however, because of the low impedance of the networkincluding coaxial cable 407 and primary 409, little noise is picked upin that network.

In FIG. 4B, signals appearing across points 401 and 402 are coupled toprimary 409 through a balanced system as contrasted with the unbalancedsystem of FIG. 4A. Conductive shield 413, which is grounded at thereceiver end as shown, prevents noise pickup in the coupling between thesignal source and the receiver primary 409. Series condenser 408 seriesresonates the circuit including primary 409, as described in connectionwith FIG. 4A. Electrostatic shield 414 reduces noise coupling betweenprimary 409 and secondary In FIG. 5, two signals having differingdirectional characteristics are derived from a single discontinuity in acar body and remote tuning of the dual antenna system is provided.

Conductive sheath 500 is connected to the boundary of the opening atpoints 501 and 502 and, as described in connection with earlierembodiments, constitutes the primary of an auto-transformer, thesecondary of which comprises conductors 503, 504 and 505 and 506 whichpass through the primary and are tightly coupled thereto. In someapplications the car body trim itself may act as the primary of theauto-transformer and the conductors may pass through that trim. Theconductors pass diagonally across opening 507 in returning for passagethrough the primary. The size of the wires is such that they do notobstruct vision through the opening, which may be the rear window. Thesecondary is center-tapped and the leads come out at conductors 508 and509 to permit center tuning of the secondary of the auto-transformer bycondenser 510. Padding condenser 511 is coupled between low-impedanceantenna output lead 512 and ground. Conductor 512 is coupled to thereceiver input circuits.

Similarly, signals are picked up between points 513 and 514 along theboundary of discontinuity 507 and are transformed in voltage, upwardly,by the autotransformer action of primary 515 and secondary conductors516 through 519 passing through the primary.

Output signals are taken from conductor 519, as shown. The secondary ofthis auto-transformer is tuned at its center by condenser 520 which isremote, as at the radio receiver, and may be ganged with the main tuningdevice of the radio receiver.

It should be noted that the car body surrounding the discontinuity 507acts as a shield for this antenna system against many electrostaticnoise signals.

In FIG. 6 the concepts set forth in connection with FIGS. 1 through 5are embodied in an otherwise functional portion of the car body. In thedisclosed embodiment the primary 600 of the auto-transformer bounds aportion of the perimeter wind-wing assembly 601 and may be a hollowconductive sheath or tube through which the secondary windings 605, 606and 607 pass. The potential difference between points 602 and 603 on thecar body edge 604 is used to drive this longer portion of this lowimpedance primary. The secondary of the auto-transformer is tunedremotely by condenser 606 which may be ganged with the receiver maintuner 617. Instead of incorporating the auto-transformer in thewind-wing assembly it may be incorporated in a rear-view mirror mountedbetween conductive body driving points 602 and 603, with the balance ofthis primary being used to support the external mirror.

The structure shown and described in FIG. 6 may be duplicated on theopposite side of the vehicle to obtain multi-directional signals andprovide nearly omnidirectional reception. Switching, automatic ormanual, may be provided, as shown using fixed contacts 607 608, 609 and610 and movable contacts 611 and 612. Energy from the secondauto-transformer, not shown, is brought to the switch through coaxialcable 613. Condensers 614 and 615 are coupling condensers bringingsignals to the receiver input circuits. Condensers 614 and 615 act aspadding condensers to apply the optimum signal to the receiver inputcircuits including trimmer condenser 616 and core tuned inductance 617.

In FIG. 7A oppositely phased signal voltages appearing at points 70 and71 on column 72 are fed to opposite extremities 73 and 74 of conductivesheath or tube 75 which acts as the primary of an impedance and voltagestep-up transformer 76 through which a secondary terminating in leads 77and 78 passes. Because primary 75 is being driven in push-pull fashionwith its center grounded its length may be doubled for better matchingof the impedance of the source and, at the same time, greater signalstep-up may be realized in the secondary. Ferrite beads 79, whichsurround sheath 75 assure increased primary-secondary coupling andpermit direct parallel tuning of the secondary of transformer 76 bycondenser 80 which is ganged with receiver input circuit tuning inductor81. Signals are injected at the high potential end of that inductorthrough coupling condenser 82 which may have a capacitance ofpico-farads. Input to the first receiver translating element is throughsecondary 83.

In FIG. 7B push-pull (or double-ended) driving of primary 84 occurs, aswith primary 75 in FIG. 7A. However, the method of coupling signals fromthe secondary winding of step-up transformer 85 through leads 86 and 87to associated radio apparatus is different from the method in FIG. 7A.Series tuning of the cicuit including the secondary of transformer 85and coupling inductances 88 and 89 is accomplished by capacitance 90which is ganged with input tuning inductor 91 to assure optimumperformance of the antenna system at each setting of the tuner in theassociated radio apparatus. Again, the antenna tuning element is locatedremotely from the conductive-body signal source.

In FIG. 7B the signal source is shown as being points 92 and 93 oncolumn 94 in which there is a discontinuity. A second signal may bederived from a second source, not shown and supplied through cables 95and 96, to which terminals 97 and 98 of primary 84 may be points 800,801 and 802, 803, respectively, by operation of slide switch 804. Thisis a balanced system with remote tuning of the antenna systemaccomplished by series condenser 805 which may be ganged with variableinductance 806. Coils 807 and 808 may be wound in layers, one on theother and connected in aiding fashion. Their self and mutual inductancemay be increased by using a ferrite core. In fact, it is possible todesign the tuning core for inductance 806 so that it has a portionalways within coils 807 and 808 despite the controlled entrance of thatcore into inductor 806 for tuning purposes.

In FIG. 9, signals may be coupled into and out of discontinuities 900and 901 which may be between the header 908 and body 909 of anautomobile. Omnidirectionality in transmission and reception may beapproached by proper coupling of energy into and out of the conductivebody through cables 902 and 903. Tuning of the combination of the bodyinductance and primary inductance 904 to a desired frequency isaccomplished by capacitance 905, which may be ganged with variabletuning inductance 906 in associated radio apparatus. Signals into andout of the system may be taken through coupling coil 907. This circuithas been used very successfully at 27 magaherz.

While specific embodiments have been described, modifications may bemade within the scope of the invention. The following claims areintended to cover such embodiments.

What is claimed is:

1. A vehicle body antenna system, including:

a windshield opening having a conductive perimeter and being responsiveto a radio frequency field to produce at points across the perimeter apotential at said radio-frequency;

radio frequency circuits remote from said discontinuity and forming apart of associated radio apparatus;

coupling means including a secondary winding directly connected toat-least-one point of the conductive perimeter and juxtaposed t0at-least-one portion thereof to form therewith a transformer with asingle turn primary; and,

tuning means coupled to said transformer and physically positionedremote from said discontinuity and proximate to said radio frequencycircuits.

2. Apparatus according to claim 1 in which said secondary winding isconnected at its other end to a capacitor which, in turn, is connectedto a point on said conductive perimeter opposite said at-least-onepoint.

3. Apparatus according to claim 2 in which the magnitude of saidcapacitor is in the order of 0.01 microfarads.

4. Apparatus according to claim 1 in which said secondary windingcomprises first and second sections each having a winding directionopposite from the other section and each section juxtaposed to adifferent portion of said conductive perimeter from said other section.

5. Apparatus according to claim 1 in which said radio frequency circuitsincludes tuning apparatus, said tuning apparatus being mechanicallycoupled to said tuning means.

1. A vehicle body antenna system, including: a windshield opening havinga conductive perimeter and being responsive to a radio frequency fieldto produce at points across the perimeter a potential at saidradio-frequency; radio frequency circuits remote from said discontinuityand forming a part of associated radio apparatus; coupling meansincluding a secondary winding directly connected to at-least-one pointof the conductive perimeter and juxtaposed to at-least-one portionthereof to form therewith a transformer with a single turn primary; and,tuning means coupled to said transformer and physically positionedremote from said discontinuity and proximate to said radio frequencycircuits.
 2. Apparatus according to claim 1 in which said secondarywinding is connected at its other end to a capacitor which, in turn, isconnected to a point on said conductive perimeter opposite saidat-least-one point.
 3. Apparatus according to claim 2 in which themagnitude of said capacitor is in the order of 0.01 microfarads. 4.Apparatus according to claim 1 in which said secondary winding comprisesfirst and second sections each having a winding direction opposite fromthe other section and each section juxtaposed to a different portion ofsaid conductive perimeter from said other section.
 5. Apparatusaccording to claim 1 in which said radio frequency circuits includestuning apparatus, said tuning apparatus being mechanically coupled tosaid tuning means.